Royal Dutch Shell PLC has become the latest company to abandon efforts to turn Western Slope oil-shale into oil, joining a long line of companies in a boom and bust cycle in the region. The company said energy markets have changed since the project started in 1982, and the company no longer wants to continue efforts to turn oily shale rock into liquid by heating the rock and pumping out the oil. Chevron stopped its oil-shale research in Rio Blanco County in February 2012.

"We are exiting our Colorado project to focus on other opportunities," Shell spokeswoman Kelly op de Weegh said. "Our focus is to work with our staff and contractors to safely stop research activities and close the site."

Efforts to squeeze the oil from the shale in the Rockies stretch back decades. An oil shale boom in Colorado in the early 1980s went bust when oil prices dropped and government subsidies dried up. People still refer to "Black Sunday," May 2, 1982, when Exxon Mobil Corp. shut down a $5 billion project near the West Slope town of Parachute, throwing 2,200 people out of work.